1. Field of the Invention
The present invention relates generally to microhardness testers for measuring hardness of a material sample, and more particularly to a device for enabling a series of material samples to be efficiently tested in succession by quickly positioning a test surface of the sample in a focal plane of an objective lens of the microhardness tester.
2. Description of the Related Art
Microhardness testers measure the hardness of a sample material, most commonly a metal, ceramic or composite sample, by deforming a test surface of the sample with a standardized indenter under a known test load to produce an indentation in the test surface, observing a size or depth of the indentation, and correlating the observed size or depth to a predetermined measurement scale. The Vickers, Knoop, Rockwell, and Brinell hardness tests are well-known examples of standardized hardness tests. Microhardness testers are often used in quality control laboratories to check surface treatments such as case hardening of steels, electrodeposited coatings, paint films, and various mechanical and thermal treatments of surface layers. Consequently, samples of various shapes and sizes are encountered, including spherical, cylindrical, and flat samples.
Some microhardness testers, such as the Leica VMHT microhardness tester, are essentially in the form of a microscope that is equipped with indentation means. Accordingly, these instruments include one or more magnifying objective lenses for accurately observing and measuring indentations left on the test surface, and a z-stage for moving the sample relative to an optical axis of a chosen objective lens. The z-stage is adjustable horizontally back-and-forth and side-to-side to locate an indentation within the optical field of view and vertically to position the test surface in the focal plane of the objective lens. The sample is seated in an anvil or secured in a clamp, which in turn may be fastened to the z-stage of the instrument. Anvils are generally designed to cradle the sample in place; for example, V-shaped anvils are common for holding cylindrical samples to test the outer diameter surface of the sample. Various clamps are also available, including a universal clamp and measuring device available from Wilson Instruments of Newport Beach, Calif., that includes an adjustable swivel-mounted stage for supporting a sample and moving the sample relative to a pair of overhead detent members for leveling an upper test surface of the sample by engagement of the test surface with the detent members. Under this design, the test surface can be made level even though a bottom surface of the sample contacting the swiveling stage is not parallel to the test surface.
Heretofore, technicians operating a microhardness tester to test a series of like-sized samples in succession have been slowed by the need to position a test surface of each new sample in a focal plane of the objective lens by adjustment of the instrument z-stage, particularly where slight variations in sample height exist. Where a large number of samples must be tested, as in the case of a production run of manufactured parts, time delays associated with hardness testing can aggregate to significant levels.
Therefore, it is an object of the present invention to provide a device that enables an operator to quickly position a test surface of a sample in a focal plane of a microhardness tester.
It is another object of the present invention to provide a device that enables an operator to more efficiently measure a series of samples by quickly positioning a test surface of each sample in a focal plane of a microhardness tester without the need to readjust a z-stage of the microhardness tester for each measurement.
It is a further object of the present invention to provide a device satisfying the above objects that is easy and inexpensive to manufacture, and that is adaptable for use with microhardness testers presently in use.
In accordance with the present invention, a device comprises a frame having a base that attaches to a z-stage of a microhardness tester under a chosen objective lens. The frame also includes upstanding front and rear walls connected by a bridge wall spaced vertically from the base. The front and rear walls of the frame each have an inwardly protruding detent rail defining an engagement surface on an underside of the detent rail, wherein the respective engagement surfaces lie in a common plane. A stage is provided between the front and rear walls for carrying a test sample with its test surface facing the engagement surfaces of the detent rails, with the stage preferably being mounted on a swivel connection.
The device further comprises means for moving the stage between a test position wherein the test surface is flush with the engagement surfaces on the detent rails, and a released position wherein the test surface is out of surface-to-surface engagement with the engagement surfaces. The particular means for moving the stage can take various forms. In a first embodiment, an automatic arrangement is disclosed wherein the stage is connected to a core rod of a solenoid, whereby the stage is moved when the solenoid coils are energized. In a second embodiment, the stage is connected to a guided member threadably mated in a guide sleeve, and an automatic driver such as a linear motor acts on a radial lever on the guide member to rotate the guide member to achieve axially directed displacement. In a third embodiment similar to the second embodiment, the radial lever extends through an opening in the front wall of the frame for manual operation. Other means for moving the stage, including pneumatic pistons, are also contemplated.
The frame itself is preferably elongated in a lateral direction and the stage resides within an opening in the bridge wall when in the released position, whereby the bridge wall supports more than one test sample moving in a lateral direction through the frame. To facilitate movement of samples laterally through the frame, a pair of PTFE slider strips on which the samples can slide are provided on the bridge wall. A pair of spring strips are provided, one along the inside of the front wall and one along the inside of the rear wall, with spring stops arranged to align a sample on the stage and to maintain spacing between the sample on the stage and adjacent test samples within the frame.
In use, the device is attached to the z-stage of the microhardness tester and the z-stage is adjusted to bring the engagement surfaces of the detent rails coplanar with a focal plane of the objective lens. The operator manually slides a stream of samples through the frame, thereby aligning one of the samples on the stage for testing. The stage is moved automatically or manually to bring the test surface of the sample into contact with the engagement surfaces, thereby positioning the test surface in the focal plane. After testing is completed, the stage is returned to its released position so that the next sample can be aligned with the stage and the testing procedure can be repeated.